Reputation: 1001

Difference between regex [A-z] and [a-zA-Z]

I am using a regex to program an input validator for a text box where I only want alphabetical characters. I was wondering if [A-z] and [a-zA-Z] were equivalent or if there were differences performance wise.

I keep reading [a-zA-Z] on my searches and no mention of [A-z].

I am using java's String.matches(regex).

Upvotes: 97

Answers (6)

Martijn Courteaux

Reputation: 68857

When you take a look at the ASCII table, you will see following:

A = 65
Z = 90
a = 97
z = 122

So, [A-z] will match every char from 65 to 122. This includes these characters (91 -> 96) as well:

[\]^_`

This means [A-Za-z] will match only the alphabet, without the extra characters above.

Upvotes: 26

Donut

Reputation: 112825

[A-z] will match ASCII characters in the range from A to z, while [a-zA-Z] will match ASCII characters in the range from A to Z and in the range from a to z. At first glance, this might seem equivalent -- however, if you look at this table of ASCII characters, you'll see that A-z includes several other characters. Specifically, they are [, \, ], ^, _, and ` (which you clearly don't want).

Upvotes: 163

Michael Borgwardt

Reputation: 346317

Take a look at the ASCII chart (which Java characters are based on): there are quite a few punctuation characters situated between Z and a, namely these:

[\]^ _`

Upvotes: 4

a'r

Reputation: 36999

The square brackets create a character class and the hyphen is a shorthand for adding every character between the two provided characters. i.e. [A-F] can be written [ABCDEF].

The character class [A-z] will match every character between those characters, which in ASCII includes some other characters such as '[', '\' and ']'.

An alternative to specifying both cases would be to set the regular expression to be case-insensitive, by using the /i modifier.

Upvotes: 8